Analysis of resonant fast ion distributions during combined ICRF and NBI heating with transients using neutron emission spectroscopy

摘要

This paper studies the deuterium distributions from 2nd harmonic ICRF heating at JET using neutron emission spectroscopy data from the time of flight spectrometer TOFOR. The fast deuterium distributions are obtained over the energy range 100 keV to 2 MeV. Specifically, we study how the how the fast deuterium distributions vary as ICRF heating is used alone as well as in combination with NBI heating. When comparing the different heating scenarios we observed both a difference in the slope of the distributions as well as in their absolute level. In the case of ICRF heating alone, the slope is Maxwellian-like over the entire energy range studied, while for the combined ICRF + NBI heating we observe a non-Maxwellian slope, which flattens out above 0.5 MeV . Comparisons are made with corresponding distributions calculated with the code PION. We find a good agreement between the measured distributions and those calculated with PION, both in terms of their shapes as well as their amplitudes. However, we also identified a period with an inverted fast ion distribution, which showed large disagreements between the modeled and measured results. Resonant interactions with tornado modes, i.e. core localized Toroidal Alfven Eigenmodes, are put forward as a likely explanation for the inverted distribution.